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How do you find gain margin and phase margin?
The gain margin is the factor by which the gain must be multiplied at the phase crossover to have the value 1. The phase crossover occurs at 0.010 Hz and so the gain margin is 1.00/0.45=2.22. The phase margin is the number of degrees by which the phase angle is smaller than −180° at the gain crossover.
How do you find the gain margin on a Bode plot?
It is usually expressed as a magnitude in dB. We can usually read the gain margin directly from the Bode plot (as shown in the diagram above). This is done by calculating the vertical distance between the magnitude curve (on the Bode magnitude plot) and the x-axis at the frequency where the Bode phase plot = 180°.
How is the gain margin calculated in dB?
The gain margin Gm is defined as 1/G where G is the gain at the -180 phase crossing. The gain margin in dB is derived by Gm_dB = 20*log10(Gm) The phase margin Pm is in degrees. The loop gain at Wcg can increase or decrease by this many dBs before losing stability.
Is the stability margin the same as the gain margin?
Yes – you have made a severe “conceptual mistake” in speaking always of the “systems phase and gain”. Normally, we use the term “system” for a working system – that means: Closed-loop. However, the stability margins (PM and GM) are defined for the LOOP GAIN.
When is system gain margin and phase margin negative?
When the System/OLTF phase is -180° but System Magnitude > 1. Thereby making Gain Margin negative. I was able to correlate a physical meaning to this condition as the same would lead to a positive feedback condition with Gain > 1 thereby leading to Unbounded output and hence instability. When the System Magnitude = 1 but System Phase > − 180°.
What should the gain margin be at 180 degrees?
Here is simplest answer At -180 degrees, gain must be below 0dB to avoid positive feedback and oscillation. The amount of dB below 0dB at -180 degree is the gain margin. If the amp is -15dB at -180. The gain margin would be 15dB